Apparatus and methods for processing ceramic mold and core materials

ABSTRACT

Apparatus for processing ceramic mold and core materials of the type containing ceramic flours, gel binder, and agglomerated gelbound flour particles utilizes a pair of oppositely rotating, closely spaced rolls having generally cylindrical surfaces with high coefficients of friction. The opposed cooperating surfaces of the spaced-apart rolls move in a like direction but with significantly different velocities to finely divide the agglomerated materials.

United States Patent inventor Herbert Greenewnld, Jr.

4296 Brlunton Road, Upper Arlington, Ohio 43220 Appl. No. 38,105

Filed May 18, 1970 Patented Nov. 23, 1971 APPARATUS AND METHODS FOR PROCESSING CERAMIC MOLD AND CORE MATERIALS 7 Claims, 8 Drawing Figs.

U.S. Cl 241/3, 241/227, 241/235 Int. Cl B021: 4/02 Field 01' Search 241/3, 30,

[ 56] References Cited UNITED STATES PATENTS 1,308,007 6/1919 Forsyth 241/227 1,743,623 1/1930 Ross 241/235 X 2,890,839 6/1959 Heller 241/3 Primary Examiner--Granvi1le Y. Custer, Jr. Auorneys- Daniel H. Dunbar and Cennamo, Dunbar &

Kremblas ABSTRACT: Apparatus for processing ceramic mold and core materials of the type containing ceramic flours, gel binder, and agglomerated gel-bound flour particles utilizes a pair of oppositely rotating, closely spaced rolls having generally cylindrical surfaces with high coefficients offriction. The opposed cooperating surfaces of the spaced-apart rolls move in a like direction but with significantly different velocities to finely divide the agglomerated materials.

PATENTEnuuv 23 um NVEN ENEW FIG. 2

I TOR. HERBERT GRE ALD,JR.

APPARATUS AND METHODS FOR PROCESSING CERAMIC MOLD AND CORE MATERIALS SUMMARY OF THE INVENTION The apparatus of the present invention for processing ceramic materials is basically comprised of a pair of driven rolls that are positioned so that their cooperating opposed faces are spaced apart relative to each other a distance in the range of approximately 0.002 to 0.040 inch. The cooperating surfaces of the spaced-apart rolls are each provided with at least the minimum surface roughness necessary to develop a tightly adhered retained film of the processed ceramic materials on the rolls. The rolls are operated at a significant surface speed difi'erential. The minimum satisfactory differential is developed from relative surface having a ratio of approximately 4:]; the differential is normally preferably approximately 8:] or greater and the upper limit generally is determined by the load capacity of the included roll bearing support components. Mold and core materials of the type described are finely divided in the apparatus by a novel materials shearing action. The so-processed ceramic materials are then further processed, as by pressing, into mold or core forms for use in metal casting. In the pressed fonn such processed materials provide molds and cores with significantly improved surface definition and increased near-surface strengths using only moderate forming pressures.

DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are partially sectioned schematic side and end views, respectively, of a preferred embodiment of the apparatus of this invention;

FIG. 3 is elevational view of a preferred bearing support arrangement for the grinding roll components of the apparatus of FIGS. 1 and 2;

FIGS. 4 and 5 are enlarged sectional views schematically illustrating the processing achieved with the instant invention;

FIGS. 6 and 7 schematically illustrate materials processing and mold and core construction characteristics associated with known apparatus and methods for processing gel-type ceramic materials into useful mold and core forms; and

FIG. 8 is an enlarged sectional view schematically illustrating mold and core construction characteristics developed by the practice of the present invention.

DETAILED DESCRIPTION The term gel-type ceramic material" is used extensively throughout this description and as employed herein it basically refers to one type of ceramic composition useful for making molds and cores for precision metal castings. More specifically, the term refers to materials essentially comprised of ceramic flours and a gel binder. Examples of such ceramic flours are -325-mesh alumina, silica, carbon, zircon, and other comparable refractory materials; examples of the gel binder include bentonite, resins, sodium and potassium silicates, hydroxide gels, silica gels, and the like, normally with combined water or other suitable liquid.

A preferred embodiment of apparatus incorporating the instant invention is referenced generally as 10 in the drawings and is essentially comprised of a grinder unit 11, a materials feed unit 12, and a conveyor unit 13. Units 12 and 13 are of conventional construction. Feed unit 12 normally is comprised of a hopper 14 for containing a supply of gel-type ceramic material 15 with included agglomerated particles and a vibrator unit 16 for distributing the contained material 15 uniformly into conveyor unit 13. Conveyor unit 13 normally is comprised of an endless conveyor belt 17, drive and support rolls l8 and 19, and variable speed drive 20. A casing 21 is usually included with unit 13 to minimize spillage and loss of material being conveyed into grinder unit 11 through the spoutlike opening 22 in casing 21.

Grinder unit ll of apparatus 10 is essentially comprised of opposed rolls 23 and 24, a motive power source such as electric motor 25, and a drive such as roller chain drive 26 for coupling rolls 23 and 24 to motor 25 in driven relationship. Rolls 23 and 24 are carried by supports 27 and 28 secured to structural framework within the housing 29 of apparatus unit 11. Chain drive 26 in addition to the basic roller chain also includes drive sprockets connected to rolls 23 and 24 and an idler sprocket 30. The elements of the roller chain drive 26 are arranged in cooperating relation so that rolls 23 and 24 are rotated in the illustrated opposite rotational directions. Apparatus 10 also includes a compartment 31 within grinder unit 11 for receiving and containing ceramic material 15 after it has been processed through grinder rolls 23 and 24. A conventional door 32 is provided for access to the interior of compartment 31.

Since it is important that the spaced-apart relationship of rolls 23 and 24 specified for obtaining the advantages of this invention be maintained at all times, rolls 23 and 24 must be adequately supported. FIG. 3 details one form of support 27 or 28 suitable for this purpose. The illustrated support 28 in that drawing is comprised of rigid end bars 33 and 34 for supporting pillow block bearings 35 and 36 that engage the rotational end shaft of rolls 23 and 24 in the manner shown. Structural tie members 37 and 38, each normally in the fonn of a mild steel beam having a H-shaped cross section, are preferably welded at each end to one of end bars 33 or 34 in a conventional manner. It is preferred that the tie members 37 and 38 be parallel to and be symmetrically positioned relative to the line 39 that intersects the axes of rotation of rolls 23 and 24 at right angles. Also, it is important that the cross-sectional areas of tie members 37 and 38 each be sufficiently great so that such members do not, by reason of applied tensional forces, act as springs and permit linear displacement of rolls 23 and 24 relative to each other during materials processing. All forces reacted into rolls 23 and 24 as a result of processing ceramic materials between the rolls impart nearly equal and symmetrically applied tensional forces to each of tie members 37 and 38. The desired spaced-apart relationship between rolls 23 and 24 and relative to their opposed cooperating surfaces is readily maintained by the illustrated support construction. corrosion It is also important that the cylindrical surfaces of rolls 23 and 24 each be provided with a roughened, wear-resistant surface finish if proper processing by apparatus 10 is to be achieved. In general rolls 23 and 24 have been made of steel and one form of satisfactory surface finish has been obtained by depositing tungsten carbide particles thereon by means of an atomic hydrogen torch. Also, in some instances, suitable roll surface finishes can be achieved by selective etching of the roll metal, as by prolonged weathering or by corrosion attack attributed to ingredients comprising the processed ceramic materials. Excessive roughening of the roll surfaces, as by a conventional machine tool knurling operation, is not desired. The optimum degree of roughening required is best described as being just sufi'tcient to retain a tightly adhered film of the finely divided gel-type ceramic being processed entirely over the roll surfaces used for carrying out the grinding operation without any of the roll metal projecting above the surface of the ceramic layer.

As pointed out above, in operating the rolls 23 and 24 in grinder unit 11, it is preferred that the opposed roll surfaces be spaced apart approximately from 0.002 to 0.040 inch in processing most gel-type ceramic materials and that that spacing be maintained. Also, it is preferred that the surface velocities of fast roll 23 and of slow roll 24 be maintained at a ratio in the range of 4:1 minimum to 8:1 or even greater if possible. The velocity differential may be developed by different roll diameters, by different roll rotational speeds, and by combinations thereof. In any event, the diameter and rotational speed values finally selected for the rolls 23 and 24 in a particular unit 11 are determined with consideration of the amount of material to be processed per unit time and the load capacity of the bearing assemblies 35, 36 provided in or available for the equipment.

The processed gel-type ceramic material as it is taken from discharge of rolls 23 and 24 has a very fine texture and feels to the hand like good cake flour mix. It is capable of being pressed into mold or core forms under moderate pressures, such as I p.s.i., to given excellent surface definition in the fonned mold or core and also excellent strength. The shearing action by which this fine texture is achieved is illustrated schematically in FIG. 4 of the drawings. FIG. 5 more clearly illustrates the tightly adhered film of gel-type ceramic that is retained on the roll surfaces to at least in part obtain the advantages associated with this invention.

FIGS. 6 and 7 schematically illustrate the problems that the present invention overcomes by reason of the improved processing of gel-type ceramic materials for use in molds and cores for metal casting applications. FIG. 6 illustrates a section of a mold 40 that was press fonned at moderate pressures using gel-type ceramic compositions having contained agglomerates such as are obtained in the normal mixing procedures for this type of material. Each of the agglomerates in the mixed composition has a tendency to form an air-dried or laminated shell on its surface which makes it very difficult to cause these entities to knit together under pressure. The failure to knit causes the pressed mold 40 to have surface deficiencies and zones of weakness at the globule or platelet boundaries. Unless extremely high pressures are used (e.g. l0,000 p.s.i. or greater), each agglomerated entity retains its external shape in part although deformed, and this in turn causes the surface of the mold or core to have pores or recesses of substantial size. See FIG. 6. This processing deficiency is believed to be the primary reason why it has been common in the past to utilize slurry-type materials when it has been desired to fonn molds having smooth surfaces. Another type of processing deficiency is illustrated schematically in FIG. 7. In that illustration rolls 41 ans 42 are rotated with a low surface velocity differential or with roll surfaces having low coefficient of friction with the ceramic material being processed and the apparatus therefore operates to essentially merely just flatten the agglomerated particles contained in the processed material. When incorporated into a mold or core by forming at moderate pressures, the flattened globules or balls behave much in the same manner as the unprocessed (not finely divided) materials.

FIG. 8, by way of comparison, schematically illustrates the surface and homegeneity characteristics obtained in a mold or core 43 formed at moderate pressures using gel-type ceramic compositions that have been processed in accordance with the instant invention. It can be readily concluded that the hereinafter claimed invention clearly produces unobvious advantages over known apparatus and methods for processing gel-type ceramic mold and core materials.

What is claimed is:

1. In apparatus for processing gel-type ceramic materials having contained agglomerates of flourlike particles and gel into finely divided form, in combination:

a. Drive means, and

b. A pair of parallel rolls having generally cylindrical surfaces driven by said drive means in opposite rotational directions and with a surface velocity ratio greater than approximately 4:1, said roll cylindrical surfaces being closely spaced apart at opposed surface regions driven in a like linear direction and each having a surface roughness sufficiently great to retain a tightly adhered film of processed gel-type material thereon at said surface velocity ratio.

2. The apparatus defined by claim 1, wherein said pair of parallel rolls are spaced apart a distance in the range of approximately 0.002 inch to 0.040 inch at said opposed surface regions.

3. The apparatus defined by claim 1, wherein said pair of parallel rolls surface velocity ration is at least approximately 8:1.

4. The apparatus defined by claim I, wherein there is additionally included a pair of bearing support assemblies supporting said pair of parallel rolls, each said bearing support assembly being comprised of a pair of bearing means cooperating with said pair of parallel rolls, a pair of opposed rigid bars supporting said bearing means, and a pair of tie bars connecting said pair of opposed rigid bars to each other, said pair of tie bars bars being oriented parallel to and positioned at equal distances from a transverse line intersecting the axes of rotation of said pair of parallel rolls at right angles and at said bearing means.

5 In a method of processing gel-type ceramic materials having contained agglomerates of flourlike particles and gel into useful fonns for making metal casting molds and cores, the step of shearing agglomerated flourlike particles of a gel-type ceramic material between opposed closely spaced-apart surfaces of retained films of said gel-type ceramic material moved relative to each other at a differential velocity based on a velocity ratio greater than approximately 4:] to thereby form a finely divided gel-type ceramic material.

6. The method defined by claim 5, wherein said finely divided gel-type ceramic material is additionally press formed into a shape using moderate compression pressures.

7. The method defined by claim 5, wherein said differential velocity is based on a velocity ratio that is at least approximately 8: l. 

2. The apparatus defined by claim 1, wherein said pair of parallel rolls are spaced apart a distance in the range of approximately 0.002 inch to 0.040 inch at said opposed surface regions.
 3. The apparatus defined by claim 1, wherein said pair of parallel rolls surface velocity ration is at least approximately 8:1.
 4. The apparatus defined by claim 1, wherein there is additionally included a pair of bearing support assemblies supporting said pair of parallel rolls, each said bearing support assembly being comprised of a pair of bearing means cooperating with said pair of parallel rolls, a pair of opposed rigid bars supporting said bearing means, and a pair of tie bars connecting said pair of opposed rigid bars to each other, said pair of tie bars bars being oriented parallel to and positioned at equal distances from a transverse line intersecting the axes of rotation of said pair of parallel rolls at right angles and at said bearing means.
 5. In a method of processing gel-type ceramic materials having contained agglomerates of flourlike particles and gel into useful forms for making metal casting molds and cores, the step of shearing agglomerated flourlike particles of a gel-type ceramic material between opposed closely spaced-apart surfaces of retained films of said gel-type ceramic material moved relative to each other at a differential velocity based on a velocity ratio greater than approximately 4:1 to thereby form a finely divided gel-type ceramic material.
 6. The method defined by claim 5, wherein said finely divided gel-type ceramic material is additionally press formed into a shape using moderate compression pressures.
 7. The method defined by claim 5, wherein said differential velocity is based on a velocity ratio that is at least approximately 8:1. 